The present invention relates generally to electronic components such as connectors, switches and sensors for conducting electrical current. In particular, it relates to such components useful in various types of machines and other applications which require electronic devices for their proper operation. More specifically, the electronic component is a pultruded composite member having a plurality of small generally circular cross section conductive fibers in a polymer matrix where the fibers are oriented in a direction parallel to the axial direction of the member and are continuous from one end of the member to the other with one end of the member having a fibrillated brush-like structure. The devices described herein are particularly well suited for low energy electronic/micro electronic signal level circuitry typified by contemporary digital and analog signal processing practices. Typical of the type of machines which may use such electronic devices are electrostatographic printing machines.
In electrostatographic printing apparatus commonly used today a photoconductive insulating member is typically charged to a uniform potential and thereafter exposed to a light image of an original document to be reproduced. The exposure discharges the photoconductive insulating surface in exposed or background areas and creates an electrostatic latent image on the member which corresponds to the image contained within the original document. Alternatively, a light beam may be modulated and used to selectively discharge portions of the charged photoconductive surface to record the desired information thereon. Typically, such a system employs a laser beam. Subsequently, the electrostatic latent image on the photoconductive insulating surface is made visible by developing the image with developer powder referred to in the art as toner. Most development systems employ developer which comprises both charged carrier particles and charged toner particles which triboelectrically adhere to the carrier particles. During development the toner particles are attracted from the carrier particles by the charged pattern of the image areas of the photoconductive insulating area to form a powder image on the photoconductive area. This toner image may be subsequently transferred to a support surface such as copy paper to which it may be permanently affixed by heating or by the application of pressure.
In commercial applications of such products, the photoconductive member has typically been configured in the form of a belt or drum moving at high speed in order to permit high speed multiple copying from an original document. Under these circumstances, the moving photoconductive member must be electrically grounded to provide a path to ground for all the spurious currents generated in the xerographic process. This has typically taken the form of a ground strip on one side of the photoconductive belt or drum which is in contact with a grounding brush made of conductive fibers. Some brushes suffer from a deficiency in that the fibers are thin in diameter and brittle and therefore the brushes tend to shed which can cause a problem in particular with regard to high voltage charging devices in automatic reproducing machines in that if a shed conductive fiber comes in contact with the charging wire it has a tendency to arc causing a hot spot on the wire resulting in melting of the wire and breaking of the corotron. This is destructive irreversible damage requiring unscheduled service on the machine by a trained operator. Also, the fiber can contaminate the device and disrupt uniformity of the corona charging.
Furthermore, in commercial applications of such products it is necessary to distribute power and/or logic signals to various sites within the machine. Traditionally, this has taken the form of utilizing conventional wires and wiring harnesses in each machine to distribute power and logic signals to the various functional elements in an automated machine. In such distribution systems, it is necessary to provide electrical connectors between the wires and components. In addition, it is necessary to provide sensors and switches, for example, to sense the location of copy sheets, documents, etc. Similarly, other electrical devices such as interlocks, etc. are provided to enable or disable a function.
The most common devices performing these functions have traditionally relied on metal-to-metal contacts to complete the associated electronic circuit. While this long time conventional approach has been very effective in many applications, it nevertheless suffers from several difficulties. For example, one or both of the metal contacts may be degraded over time by the formation of an insulating film due to oxidation of the metal. This film may not be capable of being pierced by the mechanical contact forces or by the low energy (5 volts and 10 milliamps) power present in the circuit. This is complicated by the fact that according to Holm, Electric Contacts, page 1, 4th Edition, 1967, published by Springer-Verlag, no amount of force if the contacts are infinitely hard can force contact to occur in more than a few localized spots. Further, corroded contacts can be the cause of radio frequency interference (noise) which may disturb sensitive circuitry. In addition, the conventional metal to metal contacts are susceptible to contamination by dust and other debris in the machine environment. In an electrostatographic printing machine, for example, toner particles are generally airborne within the machine and may collect and deposit on one or more such contacts. Another common contaminant in a printing machine is a silicone oil which is commonly used as a fuser release agent. This contamination may also be sufficient to inhibit the necessary metal-to-metal contact. Accordingly, the direct metal-to-metal contact suffers from low reliability particularly in low energy circuits. To improve the reliability of such contacts, particularly for low energy applications, contacts have been previously made from such noble metals as gold, palladium, silver and rhodium or specially developed alloys such as palladium nickel while for some applications contacts have been placed in a vacuum or hermetically sealed. In addition, metal contacts can be self-destructive and will burn out since most metals have a positive coefficient of thermal conductivity and as the contact spot gets hot due to increasing current densities it becomes more resistive thereby becoming hotter with the passage of additional current and may eventually burn or weld. Final failure may follow when the phenomena of current crowding predominates the conduction of current. In addition to being unreliable as a result of susceptibility to contamination, traditional metal contacts and particularly sliding contacts owing to high normal forces are also susceptible to wear over long periods of time.